Method of preparing difluoramine



Dec. 27, 1966 E. A. LAWTON ET AL Filed Sept. 15, 1959 l2 'r FLUORINE HFFLOWM ETER R EACTOR ABSORPTION N2 ll VACUUM PUMP OUTLET l6 WASTE IAUXILARY 2 SULPHURIC FLUORINE HF ACID ABSORPTION ABSORPTION TFAP 2oFlG.l

REACTOR LIQUID 30 v FIG-2 INVENTORS EMIL A. LAWTON JOHN G. WEBER BY firmg yywommu ATTORNEY United States Patent F Inc.

Filed Sept. 15, 1959, Ser. No. 840,066 4 Claims. (Cl. 23-356) Thepresent invention is directed to a novel method of preparingdifluoramine and preparing tetrafluorohydrazine therefrom. Moreparticularly, the invention is directed to a fluorination process ofpreparing difiuoramine and a catalytic process of preparingtetrafluorohydrazine from the prepared difiuoramine.

The products of the processes herein described find use as storableoxidizers and monopropellants for use in rocket engine applications and,further, are useful in preparing intermediates useful in the preparationof other compounds containing a nitrogen-fluorine bond. The processherein disclosed is cheaper than the only known prior art process due tothe fact that the methods are carried out at ambient temperatures andpressures and the fact that better yields are obtainable.

Tetrafiuorohydrazine which is made by the herein described method hasrecently been reported in the Journal of the American Chemical Society,vol. 80, at p. 5004 (1958). It was prepared by the reaction of NF withmetals at temperatures of 350 to 450 C. in the presence of such metalsas copper and arsenic. One particular species of the concerned method ofmaking tetrafluorohydrazine uses as a catalyst certain solid residuesfrom the distillation of fluorinated urea formed during the making ofdifluoramine by the herein disclosed process.

An object of this invention is to provide a method of makingdifluoramine.

A further object of this invention is to provide a method of makingtetrafluorohydrazine from difiuoramine.

A still further object of this invention is to provide a satisfactoryprocess of fluorinating urea and other nitrogen compounds to formdifiuoramine.

An additional object of this invention is to provide a method ofreacting difluoramine in the presence of a suitable catalyst such as acatalyst formed in the fluorination of urea, to formtetrafluorohydrazine.

A further object of this invention is to provide a method of makingmonopropellants having a nitrogen-fluorine bond.

A still further object of this invention is to provide a process ofmaking difluoramine and tetrafluorohydrazine oxidizers which are usefulas rocket propellants.

Further objects to this invention will be apparent from the followingdescription taken in conjunction with the accompanying drawing, inwhich:

FIG. 1 is a flow diagram of the process of making difluoramine;

FIG. 2 is a typical trap' apparatus for isolating quantities ofdifiuoramine; and

FIG. 3 is an apparatus for the preparation and recovery oftetrafluorohydrazine.

Basically, the preparation of difluoramine involves the steps offluorinating a nitrogen compound containing amide and imide linkagessuch as urea, biurea, biuret, aminoguanidine, diaminourea, orS-aminotetrazole by gaseous fluorine source such as fluorine gas dilutedwith an inert gas such as nitrogen and both liquid and gaseous productsare obtained which contain NF bonds. In heating the liquid productsdifluoramine is obtained along with other gases and can be purified bylow temperature fractional condensation. The tetrafiuorohydrazine is inturn prepared from difluoramine by a decomposition process entailing thetreatment of difiuoramine in the presence of Patented Dec. 2'7, 1 966certain solid materials an example of which is the solid residue fromthe above distillation of fluorinated urea.

The process of formation of difiuoramine may be illustrated by thefollowing equation:

4F: Nrn-o-NH, 2NHF, cor, 2HF

Alternatively, the reaction may be written as shown in Equation 2 sincethe bulk of the fluorine used was found in the initial liquid product.

(2) H II H2N' O-NH2 2F: H2NCF FzNH HF The Equation 3 for thedecomposition of difluoramine to tetrafluorohydrazine is:

FIGURE 1 is a flow diagram of the method of making difluoramine andshows the entry of the hereinafter described amounts of fluorine gas andnitrogen gas which are metered by valves 10 and 11 into a glass or Pyrexflow meter 12 which measures the rate of flow of the gases into areactor 14. The solid to be fluorinated is placed on a grid 9 in areactor 14 which is preferably of stainless steel and arranged so thatany liquid formed drops below the grid and collects in the bottom of thereactor adjacent to the gas inlet tube. Prior to the commencement ofactual fluorination the sysem shown in FIG.

1 is flushed with nitrogen and cooling baths employed liquid containingdifluoramine and the exit gas passedinto hydrogen fluoride absorbers 15and 16 which contain sodium fluoride as the absorbing agent. The gasesthen pass through a cooled U-trap 19 in which gaseous by-products arecondensed, which may contain some resid ual difluoramine, a fluorineabsorber 20 containing potas-- sium or sodium chloride and a sulfuricacid trap 21. Residual gases from the trap 21 are passed to wastethrough line 22. The trap 19 is detachable from the over-- all system.Three-way valve 18 is suitably positioned when removing trap 19 from thesystem so that vacuum pump outlet 17 may remove gases being formed inreactor 14.

It has been found that the preferred temperature within the reactor 14is approximately 0 C. The temperature may range, however, fromapproximately -30 C. to +40 C. for satisfactory results. The pressure inthe reactor 14 is generally atmospheric although it has been determinedthat a pressure range of from about one-half atmosphere to twoatmospheres is a preferable pressure range usable in the describedfluorination process. The particular time of fluorination is dependentupon the size of the sample, the gas flow rate and the particularparticle size and shape of the starting material.

The ratio of the mols of fluorine t-o mols of urea, which is a preferredstarting material, is in the range of from about 0.5:1 to about 3.0:1.About 0.8 mol of F per mol of urea is a preferred ratio. The ratio ofmols of F to mols of N flowing through flow meter 12 is in a preferredrange of from 5:1 to 7:1. The ratio of N to F may encompass a ratio of Nto F on the mol basis of from about 3:1 to 15:1. The rate of reaction ofthe fluorine and urea is practically instantaneous. Due to the reactionbeing exothermic, fluorine is passed into the reactor slowly, in thecase of the hereinafter described examples and semicarbazidehydrochloride may be employed as the starting material. Any inert gassuch as argon, krypton, nitrogen or carbon dioxide may be employed. Ifthe present invention is performed at very low pressures the inert gasesmay be dispensed with.

FIGURE 2 shows a typical trap apparatus useful in fractionating thefiuorinated nitrogen compound collected in the reactor 14 shown inFIG. 1. The liquid from reactor 14 is heated in vessel 30 to about roomtemperature and is thereby partly changed into gaseous form. The gasesare communicated to a U-trap 31 having a lower portion 33 situated in avessel 32 providing a temperature of about 80 C. Upon fractionation,i.e. condensation of particular gaseous components, at this particulartemperature the gases remaining are communicated to a U-trap 34 having abottom portion 36 in a vessel 35 held at 142 C. The remaining gases arethen communicated to a U-trap 37 having a bottom portion 39 situated ina vessel 38 having a temperature of 196 C. Flow of the gases through themultiple traps is accomplished by a pump 40. The solid materialcollected in the --142 C. trap is difiuorarnine while the solidmaterial, containing HNCO and other whitish refractory material, in the80 C. trap is usable as the catalyst material for the preparation oftetrafluorohydrazine. Care must be taken with respect to the 196 C. trapsince any solid difluoramine formed therein tends to detonatespontaneously.

Table I shows various runs involving the fiuorination of the applicablenitrogen compounds.

TABLE I Fluorine Run Mols Urea Mols F; low Time Percent No. Rate, (hrs.)F;

g./min.

0. 54 2. 7 0. 15 11.8 44. 7 0.82 3.1 0. 15 13 56. 6 0.62 2. 6 0. 15 1150. 1 1. 67 6. 3 0. 19 20. 8 53. 2 1. 67 3. 9 0.21 11. 5 48. 7 0. 150.36 0.08 3 0.35 0. 66 0. 11 3. 5 60. G 0. 20 0. 72 0. 06 4. 6 48. 3 B0. 10 0.68 1 0.18 3.8 A 0.02 0.73 1 0.27 3.0 S 0. 04 0.70 0.08 5. 3

1 Mol/hr.

wherein G is a guanidine hydrochloride, B is biurea, A is-aminotetrazole and S is semicarbazide hydrochloride, and each issubstituted for the urea of the first seven examples.

Table II shows the physical properties of the difluoramine formed by thedisclosed process and serves to ide11- tify the product formed.

(80 to 40 C.) l0g p =129l.8/t+8.058. Extrap. vapor pressure:

At 0' C. (32 F.) 48.7 p.s.i.a. At C. (68 F.) 108 p.s.i.a. At 50 C. (122F.) 397 p.s.i.a.

Density equation 1 D=l.424.00202t. Coefficient of cubical expansion 1.3X l0 C- Heat of vaporization 5.91 kcal./mol.

For purposes of further identification of the product formed thefollowing mass spectrum (Table III) using a Consolidated ElectrodynamicsModel 21-105C mass spectrometer is presented.

TABLE III Mass spectrum 0 f difluoramine Sample 1 Sample 2 Mass No.

Peak H Pattern Coef. Peak H PatternCoef.

The following detailed specific mode of practicing the present process,supplementing the data heretofore given both with regard to FIG. 1 andTable I, is as follows:

Fluorination of urea:

Urea, weight=36.3 g. (0.60 mol). Fluorine, weight=l8.4 g. (0.48mol)=0.l2 mols/hr. Fluorine nitrogen: 1 10. F luorination time=4.0 hr.Reaction bath temperature=0 C. Trap: glass, following HF absorbers,preceding F absorber; bath temperature 126 to 100 C.

The urea was dried for two days at C. The HP absorbers were charged withreagent grade sodium fluoride (dried at 300 C.). The reagent grade wasavailable as a powder and it was necessary to suspend layers of it onPyrex wool to permit the free flow of gas. The reactor contained 50.5 g.of a milky orange liquid which included difiuoramine and which wasstored in polyethylene at Dry Ice temperature. The entire contents ofthe U-trap was 6.5 cc. brown gas with an infrared spectrum indicatingonly silicon tetrafl-uoride and nitrogen dioxide. The liquid product wasfound to contain 35.0 percent total fluorine and about 15.0 percent(avenage of 14.1 and 15.8) active fluorine. Ninety percent of thefluorine used was present in the product.

Fractionation of fluorinated urea Fluorinated urea was distilled from aKel-F coated flask through Pyrex into a Pyrex U-trap cooled with liquidnitrogen. The distillation was stopped after 40 minutes, at which timeits rate was slow and the contents of the flask were entirely fluid. Themore volatile components of the distillate were transferred to a highvacuum line (about 800 cc. gas plus 0.1 ml. liquid). This mixture wasfractionated through a trap cooled to l42 C., the noncondensible portionconsisting of only silicon tetrafiuoride and carbon dioxide. Thematerial which condensed at l42 C. was fractionated through 45 C., 'll2C. and 142 C. The 45 C. condensate was mainly a very slightly volatileliquid with a small amount of gas whose infrared spectrum showed only aband at 2.9. The infrared spectrum of the 112 C. condensate, 3.9 cc.,showed bands at 4.6, 8.0, 8.6, 8.8, 9.7 (SiF and 11.0,u. The 142 C.condensate, 51.7 cc., was difluoramine, with a trace of silicontetrafiuoride and carbon dioxide. The material, noncondensible at -142C., was refractionated several times to yield mixtures of silicontetrafiuoricle and carbon dioxide with traces of difiuoramine and 6.2cc. gas, whose infrared spectrum indicated chiefly silicon tetrafluorideand tetrafluorohydrazine. The nearly pure difluoramine, 51.7 cc., wasrefraetionated through 127 C. and -l42 C. The 142 C. condensate, 1.9cc., was pure difluoramine, and the gas noncondensible at -l42 C., 5.4Co., was nearly all silicon tetrafluoride and carbon dioxide.

In a further example a major amount of difluoramine condensed out in a126 C. trap. Difluoramine can be recovered in traps within the range offrom about 120 C. to about -150 C. The particular temperatures depend onthe particular pressures employed.

FIGURE 3 shows an apparatus for obtaining tetrafluorohydrazine fromdifluoramine. It comprises a flask 41, stoppered at 42 and containing afrozen ring 43 of difluoramine which was formed in the 142 C. orthereabouts cold trap above described. Contained in the bottom of theflask 41 is a catalyst material 44 which may be the insoluble solidrefractory material from the 80 C. or thereabouts fractionalcondensation trap above described (believed to be HCNO polymers), orsolid lithium hydride, or type 304 stainless steel or gaseous perchlorylfluoride FClO or gaseous HCl. The amounts of these latter gases is notcritical. A 4:1 ratio of difluoramine to FClO is preferred. As thefrozen ring or slug 43 is melted the gas formed contacts the catalystmaterial 44 forming N F gas 45 within the flask. Yields as high as 67%have been obtained. Liquefication of this N F gas makes the materialuseful in the aforesaid rocket propellant field.

A specific example of the practice of this process is: 14.5 cc. ofdifluoramine was introduced into an ampoule containing lithium hydride(4.1 mg.) in such a manner that the difluoramine formed a solid ringabove the hydn'de. The ampoule was then stored in a Dewar containing asmall amount of liquid nitrogen so that the reactants would warm slowlyto room temperature. After 60 hours at room temperature, the gaseousproducts were removed and separated in the vacuum line. The solidproduct was tested with aqueous hydriodic acid and gave a negative testfor oxidants. The composition of the gaseous product mixture isdescribed in Table IV.

TABLE IV Gaseous products from difluoramine and lithium hydrideQuantity, Nitrogen Product cc. Method of Identification Content (as N2),cc.

N; 1. 2 Mass spectrograph 1. 2 H: 8.0 (10 N2F4 2. 5 Infrared speetrum.2. 5 HNF; 4. 4 0 2. 2 Other None Reaction products from difluoraminewith lithium hydride Product Quantity, How Isolated Method of co. S.T.P.Identification N; 3 5 Nongondensible Mass spectrum.

.3 Condensible at -142 3. 7 Noncondensible at 142 13. 7 Solid 0.Infrared spectrum.

H1 evolution.

Chemical analysis.

Noteworthy in this experiment is the smooth formation of 3.7 cc.tetrafluorohydrazine from 11.9 cc. difluoramine. This represents a 67percent yield.

For a still further example, 2 cc. of difluoramine were stored in astainless steel ampoule at room temperature. After several days it wasfound that about two-thirds of the difluoramine had been converted intotetrafluorohy- Although the invention has been described and illustratedin detail, it is to be clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of this invention being limited only bythe terms of the appended claims.

We claim:

1. A method of preparing difluoramine comprising the steps offluorinating, with elemental fluorine, a nitrogen compound selected fromthe group consisting of urea, biurea, biuret, aminoguanidine,diaminourea, S-aminotetrazole, guanidine hydrochloride, andsemicarbazide hydrochloride, heating the liquid products of saidfluorinating step and fractionally condensing gaseous products of saidheating step to obtain substantially pure difluoramine.

2. A method of preparing difluoramine comprising the steps offluorinating urea at a temperature of from about 30 C. to about 40 C.with gaseous fluorine diluted with an inert gas to produce liquidproducts, heating the liquid products of said fluorinating step andseparating by fractional condensation the gaseous products of saidheating step to obtain substantially pure difluoramine.

3. A method of preparing difluoramine comprising the steps of dryingurea, fluorinating said urea at approximately 0 C. at about atmosphericpressure with elemental fluorine, absorbing hydrogen fluoride gas formedduring the action of said urea with said fluorine, collecting liquidformed during the fluorination step, heating said liquid to form gaseouscompounds thereof and fractionally condensing said gaseous products atvarious temperatures within the range of from C. to C. wherebysubstantially pure difluoramine is present in one of the fractionscondensed.

4. A method of preparing difluoramine comprising fluorinating urea withelemental fluorine wherein the ratio of mols of fluorine to mols of ureais in the range of from about 0.5 :1 to about 3.0:1, and separating theproducts formed by said fluorination by fractionation to obtain asubstantially pure fraction of difluoramine.

References Cited by the Examiner Journal of the American ChemicalSociety, vol. 80, p. 5004, Sept. 20, 1958.

Rufl: Angewandte Chemie, vol. 46, pp. 739-742 (1933). I

Supplement to Mellors Comprehensive Treatise on Inorganic andTheoretical Chemistry, Supplement H, Part I, Longmans, Green and Co.,New York, N.Y., 1956, p. 59.

MILTON WEISSMAN, Primary Examiner.

MAURICE A. BRINDISI, OSCAR R. VERTIZ,

Examiners. E. C. THOMAS, Assistant Examiner.

1. A METHOD OF PREPARING DIFLUORAMINE COMPRISING THE STEPS OFFLUORINATING, WITH ELEMENTAL FLUORINE, A NITROGEN COMPOUND SELECTED FROMTHE GROUP CONSISTING OF UREA, BIUREA, BIURET, AMINOGUANIDINE,DIAMINOREA, 5-AMINOTETRAZOLE, GUANIDINE HYDROCHLORIDE, AND SEMICARBAZIDEHYDROCHLORIDE, HEATING THE LIQUID PRODUCTS OF SAID FLUORINATING STEP ANDFRACTIONALLY CONDENSING GASEOUS PRODUCTS OF SAID HEATING STEP TO OBTAINSUBSTANTIALLY PURE DIFLUORAMINE.